Engine lubricant formulations are specifically designed for addressing a wide range of performance characteristics. The ability of a lubricant composition to meet specific performance characteristics may vary considerably depending on the base oil used to formulate the lubricant composition. For example, a lubricant composition that includes an additive package in a Group II base oil may pass a specific engine test. However, the same additive package in a Group I base oil may fail the engine test. Ideally, if an additive package is designed to pass an engine test with the lowest grade base oil, e.g., a Group I base oil, then it is likely that the same additive package will pass the engine test with higher grade base oils, e.g., Group II, III, or IV base oils.
One engine test that provides an indication of the performance of an additive package in a base oil is the sequence IIIG engine test. In the sequence IIIG engine test, in order to meet the requirements of the latest North American engine oil specification, ILSAC GF-5, a lubricant composition must exhibit a 40° C. viscosity increase of no more than 150%, have a weighted piston deposit rating of greater than 3.5, have an average cam-plus-lifter wear of less than 60 μm, have no stuck piston rings, and have a hot oil consumption of less than 4.65 liters. The ability of a lubricant to meet all of these requirements is determined by both the base oil and the additive package. Hence, there continues to be a need for additive compositions for lubricants that provide improved engine performance in a wider variety of base oils without significantly increasing the cost of the additive package or the amount of ingredients used in the additive package.
With regard to the above, the disclosure provides a lubricant composition for lubricating an engine. The lubricant composition includes a base oil of lubricating viscosity, one or more metal dialkyldithiophosphates having more than 75 mole percent of alkyl groups derived from 4-methyl-2-pentanol, and from about 0.1 to about 2.0 percent by weight of detergent derived from an alkyl phenol or sulfurized alkyl phenol based on a total weight of the lubricant composition. An amount of the one or more metal dialkyldithiophosphates in the lubricant composition ranges from about 0.01 to about 0.10 percent by weight phosphorus based on a total weight of the lubricant composition. The lubricant composition has a total a total base number (TBN) of about 5.0 to about 10.0.
In another embodiment, the disclosure provides a method for reducing engine deposits. The method includes formulating a lubricant composition to contain a base oil of lubricating viscosity and an effective amount of synergistic additive and operating an engine on the lubricant composition. The synergistic additive includes (i) one or more metal dialkyldithiophosphates having more than 75 mole percent of alkyl groups derived from 4-methyl-2-pentanol, and (ii) from about 0.1 to about 2 weight percent of detergent derived from an alkyl phenol or sulfurized alkyl phenol, based on a total weight of the lubricant composition. The lubricant composition has a total a total base number (TBN) of about 5.0 to about 10.0.
Yet another embodiment of the disclosure provides a synergistic additive concentrate for a lubricating oil composition. The additive concentrate includes (i) one or more metal dialkyldithiophosphates having more than 75 mole percent of alkyl groups derived from 4-methyl-2-pentanol in an amount sufficient to provide 0.01 to about 0.1 percent by weight phosphorus to a fully formulated lubricant composition. Also included in the additive concentrate is (ii) a detergent derived from an alkyl phenol or sulfurized alkyl phenol, wherein a weight ratio of (i) to (ii) in the additive concentrate ranges from about 0.1:1 to about 12:1. The additive concentrate has a total base number (TBN) that is sufficient to provide a lubricant composition with a total a total base number (TBN) of about 5.0 to about 10.0.
Surprisingly and quite unexpectedly, the additive composition containing components (i) and (ii), described above, may be effective to provide a passing rating in a IIIG engine test for a Group II base oil. More specifically, the disclosed additive that includes component (i) may be surprisingly more effective in combination with a phenate detergent in a Group II base oil than one or more metal dialkyldithiphosphate having less than 75 mole percent alkyl groups derived from 4-methyl-2-pentanol. Likewise, the disclosed additive is surprisingly more effective in a Group II base oil than component (i) and other detergents in the absence of phenate detergents. Other features and advantages of the embodiments may be evident from the following detailed description.